1. Field of the Invention
The present invention relates generally to steelmaking, and more particularly to an improved apparatus and process for recovering iron from steel mill and other metallurgical process wastes by a direct reduction process.
2. Description of Related Art
Waste materials are a natural byproduct of steelmaking and other metallurgical processes, such as the refining of nickeliferous ores. Steelmaking processes employing either a basic oxygen furnace (BOF) or an electric arc furnace (EAF) typically use large amounts of scrap, much of which is galvanized. Thus, the wastes produced include a dust containing oxides of iron as well as oxides of impurities such as zinc, lead and cadmium.
EAF dust has been declared hazardous due to the high levels of lead and cadmium oxides and must therefore be collected and reprocessed in order to protect the atmosphere and groundwater. BOF dust is expected to be declared hazardous under future environmental regulations. Because of the presence of zinc and lead oxides, attempts to reclaim the iron oxides directly for reuse have not proved to be practical.
Alternatives to direct recovery of the iron oxides have been proposed. One such proposal is to pelletize the dust and to then subject it to a very high temperature for a short period of time to sinter the pellets and to volatilize the impurities. The very high temperature partially melts the iron oxide which, when it cools, rapidly forms a glass-like material which fuses the pellets together. The resultant mass is difficult to reduce and recovery of impurities is relatively ineffective.
Holley U.S. Pat. No. 3,836,353, which issued on Sep. 17, 1974, for Pellet Reclamation Process, relates to a process for recovering iron from steel mill dust, which produces hard un-fused pellets of partially reduced iron with an iron oxide surface. The present invention relates to improvements to the invention set forth in the Holley patent.